The invention relates to a hollow body or structure for heated gases subjected to positive pressure, the said hollow body comprising a rotationally symmetrical external wall and a perforated partition wall which extends substantially parallel to the external wall within the hollow body, the intermediate space between the external wall and the partition wall being filled with heat-insulating materials.
Such hollow bodies are used as pressure vessels or more particularly as tubes for example in a circuit of a gas turbine installation with a gas-cooled nuclear power reactor.
In known hollow bodies of this kind as illustrated for example in Swiss Pat. No. 242,910 (U.S. Pat. No. 2,468,902, dated May 3, 1949), the perforation of the partition wall bounding the intermediate space is provided for reasons of pressure compensation between the intermediate space and the remainder of the interior of the hollow body. As a result, the heat-insulating materials in the intermediate space are subjected not only to thermal stresses, which can result in so-called creep in the materials for example, but in cases of pressure variations in the heated gas are also subjected to mechanical stresses. For example, high pressure variations of up to 10 at/sec and above may suddenly happen. In addition to the stresses just mentioned, acoustic and other vibrations may also act on the insulating layer in the conduits.
Owing to thermal and mechanical loads on the layer of insulating material, in hitherto known hollow bodies empty spaces may be produced in the layer of insulating material in the space between the external wall and the partition wall, with the result that the layer of insulation could be gradually destroyed until the hollow body would have to be taken out of operation owing to excessive thermal stress at its external wall.